So I did some research and I found these mods that flesh out the Dark Brotherhood and Morag Tong factions:

1) Shuuda's "Morag Tong Expanded", which adds additional quests to the other Morag Tong guilds on Vvardenfell http://www.nexusmods.com/morrowind/mods/42120/?

2) Sladle's "Morag Tong-Methas Hlaalu" which adds a quest to explain the existence of a corpse in the Morag Tong headquarters http://www.nexusmods.com/morrowind/mods/28252/?

3) Vrolok's "Dark Brotherhood Headquarter," which redecorate's the Brotherhood's headquarters in Mournhold and beefs up the assassins you fight for that part of the Tribunal main quest http://www.nexusmods.com/morrowind/mods/43022/?

4) Vegtabills Threads of the Webspinner, which fleshes out the quest to collect the threads in the game

http://www.nexusmods.com/morrowind/mods/43893/?

5) Emyn's "To Serve Sithis", which allows the player to do quests for the Dark Brotherhood http://mw.modhistory.com/download-112-12879

6) Westly's "The Shrine of Mephala," which adds a full on shrine for the Morag Tong's patron Daedric Prince http://mw.modhistory.com/download-112-11326

Has anyone used these and know whether they all work together? Does anyone have any other suggestions for mods that flesh out these factions?